In the manufacture of pneumatic tires elastomeric components, some of which are reinforced by cords of textile or wire, are formed as long strips. These strips are assembled together to form a carcass subassembly in a first stage of assembly. This carcass typically has one or more cord reinforced plies, a pair of bead cores and an air impervious liner. Additional strips of material such as apexes, shoulder gum strips and chippers and chaffers may also be used in this first stage of tire assembly.
In a second stage the tread rubber and belt or breaker reinforcing structure is typically applied to the carcass after the carcass has been toroidally shaped on the tire building drum. The tread rubber can be of one homogeneous compound or more. Typically the tread is a sophisticated composite of many different rubber materials co-extruded to form a tread strip. The belt or breaker reinforcing layers generally include two layers or more of cross plies reinforced by equal but oppositely oriented cords of textiles, such as nylon or aramid or wire such as steel. Additionally, overlays or underlays of generally circumferentially oriented cords may be added as an additional layer.
Tires typically have been built using this two-stage assembly. Once assembled this uncured assembly of the components is placed in a mold to be vulcanized to form a finished tire.
High speed and efficient ways to manufacture tires require the processes to be reliable and fast. Accordingly, manufacturers of tires have experimented with and perfected many ways to improve on the basic two-stage assembly of tires.
One method described in U.S. Pat. No. 3,865,670 taught the use of an expansible and contractible transfer ring for conveying a breaker tread assembly from a building drum in a tire building machine to a tire carcass mounted on a tire shaping machine.
An improved but somewhat similar U.S. Pat. No. 3,888,720 also disclosed a separate tread breaker building drum designed to vary in size to accommodate different sizes of tires.
Similarly, the Charles E. Todd U.S. Pat. No. 3,865,669 also disclosed an expansible and contractible transfer ring for conveying a breaker-tread assembly.
Each of these prior art patents recognized that an assembly of a tread belt to a tire carcass can be accomplished off-line or separate from the carcass building machine. Once formed into a ring these tread breaker assemblies could be moved to encircle a tire carcass, the carcass inflated to contact the inner surface of the tread breaker assembly and then stitched together by a roller mechanism to form a green or uncured tire assembly to be placed into a mold.
While these assembly techniques provided efficiencies in production, none really changed the method for actually forming a tire assembly.
Conventional tire molds, whether two piece molds or segmented molds, form the tread surfaces by pressing groove forming ribs and sipe forming blades into the tread rubber as the tire is molded. As this is done the belt cords, particularly those directly under the groove-forming ribs deflect in small but noticeable undulations. These undulations create a variety of changes across the tread that actually can vary the surface or change the amount of tread rubber across the otherwise normal appearing tire. These non-uniformities can lead to mass imbalance issues, irregular wear and a variety of associated ride and handling performance issues. The goal in tire manufacturing is to minimize unpredictable non-uniformities in manufacturing while also building the tire in a very cost-efficient manner.
The object of the present invention is to provide a method that minimizes or eliminates the influence of the tread forming mold surfaces as the tire is molded.
A further object of the invention is to provide a more productive method of assembling the tread-belt or breaker reinforcing structure to the carcass.
Another objective is to change the method of how the tread forming surfaces engage the tread rubber.
Still another objective is to provide a novel apparatus for forming the tread-belt or breaker assembly and to employ that apparatus to a unique tire building system.